Bottom Line:
After 43 years, the soil irrigated with fresh water (FW) had higher AMF diversity than soils irrigated with WW.Microbial activities were significantly higher in the soils irrigated with WW than in those irrigated with FW.Therefore, as no negative effects were observed on crop vitality and productivity, it seems that the ecosystem resilience gave rise to the selection of AMF species better able to thrive in soils with higher microbial activity and, thus, to higher soil fertility.

ABSTRACTThe effects of irrigation with treated urban wastewater (WW) on the arbuscular mycorrhizal fungi (AMF) diversity and soil microbial activities were assayed on a long-term basis in a semiarid orange-tree orchard. After 43 years, the soil irrigated with fresh water (FW) had higher AMF diversity than soils irrigated with WW. Microbial activities were significantly higher in the soils irrigated with WW than in those irrigated with FW. Therefore, as no negative effects were observed on crop vitality and productivity, it seems that the ecosystem resilience gave rise to the selection of AMF species better able to thrive in soils with higher microbial activity and, thus, to higher soil fertility.

pone-0047680-g003: Bar plot showing the number of clones detected for each AM fungal sequence type in the soil irrigated with fresh water (FW) and treated wastewater (WW) 43 years after establishment.

Mentions:
There were higher number of AMF sequence types occurring exclusively in the soils irrigated with FW (GloG1, GloG6, GloG7, GloG8, GloG10, GloG11, GloG16, GloG17 and GloG19) than in those irrigated with WW (GloG4, GloG5, GloG9 and GloG15) (Fig. 3). This difference in the AMF community composition between WW and FW treatments was shown also in the CCA diagram (Fig. 4). The rest of the AMF sequence types (GloG2, GloG3, GloG12, GloG13, GloG14 and GloG18) were found in soils irrigated with either type of water. This change in the AMF community composition could have been due to selection of the types of AMF better able to proliferate and survive under the prevailing soil conditions [10]. In this sense, positive, significant correlations were observed between the urease (r = 0.642; P<0.05) and protease (r = 0.688; P<0.05) activities and the GloG18 fungal type as well as between the exchangeable P (r = 0.672; P<0.05) and GloG13 (Table 3), both AMF types appearing in the highest proportion when the soil was irrigated with WW (Fig. 3). These results were clearly represented in the CCA analysis (Fig. 4).Since changes in enzyme activities are mediated by shifts in microbial populations; it can be assumed that the reorganization of the edaphic microbial communities both in function and composition could exert a clear influence on AMF communities.

pone-0047680-g003: Bar plot showing the number of clones detected for each AM fungal sequence type in the soil irrigated with fresh water (FW) and treated wastewater (WW) 43 years after establishment.

Mentions:
There were higher number of AMF sequence types occurring exclusively in the soils irrigated with FW (GloG1, GloG6, GloG7, GloG8, GloG10, GloG11, GloG16, GloG17 and GloG19) than in those irrigated with WW (GloG4, GloG5, GloG9 and GloG15) (Fig. 3). This difference in the AMF community composition between WW and FW treatments was shown also in the CCA diagram (Fig. 4). The rest of the AMF sequence types (GloG2, GloG3, GloG12, GloG13, GloG14 and GloG18) were found in soils irrigated with either type of water. This change in the AMF community composition could have been due to selection of the types of AMF better able to proliferate and survive under the prevailing soil conditions [10]. In this sense, positive, significant correlations were observed between the urease (r = 0.642; P<0.05) and protease (r = 0.688; P<0.05) activities and the GloG18 fungal type as well as between the exchangeable P (r = 0.672; P<0.05) and GloG13 (Table 3), both AMF types appearing in the highest proportion when the soil was irrigated with WW (Fig. 3). These results were clearly represented in the CCA analysis (Fig. 4).Since changes in enzyme activities are mediated by shifts in microbial populations; it can be assumed that the reorganization of the edaphic microbial communities both in function and composition could exert a clear influence on AMF communities.

Bottom Line:
After 43 years, the soil irrigated with fresh water (FW) had higher AMF diversity than soils irrigated with WW.Microbial activities were significantly higher in the soils irrigated with WW than in those irrigated with FW.Therefore, as no negative effects were observed on crop vitality and productivity, it seems that the ecosystem resilience gave rise to the selection of AMF species better able to thrive in soils with higher microbial activity and, thus, to higher soil fertility.

ABSTRACTThe effects of irrigation with treated urban wastewater (WW) on the arbuscular mycorrhizal fungi (AMF) diversity and soil microbial activities were assayed on a long-term basis in a semiarid orange-tree orchard. After 43 years, the soil irrigated with fresh water (FW) had higher AMF diversity than soils irrigated with WW. Microbial activities were significantly higher in the soils irrigated with WW than in those irrigated with FW. Therefore, as no negative effects were observed on crop vitality and productivity, it seems that the ecosystem resilience gave rise to the selection of AMF species better able to thrive in soils with higher microbial activity and, thus, to higher soil fertility.